1. Field of the Invention
This invention relates to a brake disc rotor of a disc brake device used in a vehicle or the like.
2. Description of the Related Art
As shown in FIGS. 1 and 2, a brake disc rotor of the prior art includes a plurality of partition walls F formed only radially between disc-shaped sliding plates OP and IP to form inlet openings I, outlet openings O and radial passages H between the partition walls, respectively.
As is apparent from an oil film observation for analyzing the stream within each passage, the prior art brake disc rotor described above has some problems as mentioned in the following discussion. As shown in both of FIG. 3 showing the processed data according to a styrene particle tracer method and FIG. 4 showing a sketch of the stream based on the above description, the stream, which flows from the inlet opening I into the passage H at an approximate angle of 50.degree. from the velocity triangle composed of the velocity components in the peripheral and radial directions in the inlet opening, generates separation in the thickness direction on the suction surface side from the inlet to the outlet of the partition walls F constituting fins F, to result in a stagnation Y in a large area at the lower portion of each partition wall within the passage H constituting a ventilation hole. Therefore, a main stream area MS becomes very narrow, while a quasi-secondary stream SS occurs due to the collision against the upper surface of each partition wall and a reversed stream RS from the external portion also occurs at the upper portion of the outlet opening.
As a result, the prior art brake disc rotor has disadvantages in that since the pressure loss of the stream is large due to the narrowness of the main stream area MS, the surface heat transfer coefficient in the passage area by cooling wind is lowered to result in an undesirable efficiency in blowing and cooling of the rotor, while since the cooling area is reduced, the total quantity of heat dissipation is decreased.
This fact is more remarkable when increasing the number of sheets of fins in order to enlarge the cooling area, and particularly, there is a disadvantage in that the cross section of the inlet portion becomes small and the inflow resistance is increased.